The invention relates to a welding head for a strap binding machine including strap fixing means for fixing the overlapping strap ends that are to be welded to one another, a welding device for fusing the strap segments that are to be welded, and a pressing device for pressing the fused strap segments against a pressure part.
Strap binding machines bind packaged goods, for instance a stack of catalogs or newspapers, with a strap, such as a stable plastic strap. In order to fix this strap in its taut state about the package, a welding head is provided that makes it possible to join the two overlapping strap ends of the binding strap, which is first fed via an appropriate insertion apparatus into a frame surrounding the package, the frame then being opened and the strap being securely tautened thereabout. This occurs in that the strap ends in the overlapping region are locally fused by means of a welding device and are pressed securely against a pressure part by means of a pressing device such that the joint results in the fused region. The manner in which a binding machine works is sufficiently well known, and it is not necessary to go into greater detail about this.
A welding head of the type cited in the foregoing is known for instance from DE 199 48 880 A1. It has two clamping jaws and a pressing device arranged therebetween. The two clamping jaws and the pressing device are longitudinally movable, for which purpose provided on the welding head housing are separate guide tracks, the cross-sections of which coincide with those of the clamping jaws. Guide tracks and clamping jaws must be worked very precisely for a precise longitudinal guide. Furthermore, in order for the clamping jaws to run smoothly and with low friction in the guide tracks, lateral flat lubrication pockets are formed in the clamping jaws and/or in the pressing device. It is evident that the longitudinal guides for the longitudinally moving parts are very complex in terms of design, which also has a negative effect on the total cost of the welding head. Another disadvantage is constantly assuring continuous lubrication in order to ensure that the longitudinally moving parts run smoothly. The open guide tracks furthermore tend to become soiled which is also disadvantageous.